Facsimile transmission



oct. 25, 1932.

F. SCHRTER FACS IMILE TRAN'SMI SS ION Filed Jan. 15. 1930 mm scHRTER BY WW ATTORNEY Patented Oct. 25, 1932 UNITED fs TATE'Sr FRITZ scHR'rEnoF BERLIN, GERMANXASSIGNOR To TELIUNKENGEsELLscIIAI-T DRAHTLOSE TELEGRAPHIE M. B. .H`., GERMANY Applicationled January 13,1930, Serial No.

'Experience with short'waves, particularly ofthe order of magnitude of l5 m. length, has vrevealed the yfact ,that telegraphicy signs of very short duration, lfor instance 1/100() sec., do not always arrive at the'receiver in a sharpcondtion, but are often widened. In addition .there are other'disturbing infiuences, for instance path changes of the wave travelling between transmitter and receiver, which causetemporal displacements in the reception of signals resulting,y in the transmission of pictures, in a jagging or ravelling of smooth edges. These disturbing yinfluences causing picture distortion constitute therefore a great handicap in the way of a rapid picture and facsimile telegraphy over short waves, ina-smuch as it becomes necessary to reduce the rotating speed of the picture drum, hence the speed of transmission, to a degree which ren dersthe widening or jaggingharmless by diminishing them approximately to the width of a picture point.

This invention proposes arsolution which does away with the described deficiency by adaptation to the peculiarities-of short-wave transmission and permits an undiminished speed of transmission. To this endthe news or documents to be facsimiled are mounted on a number of reduced-speed transmitting and receiving drums and to eachfcombination of this kind is assigned a separate transf mission channel with a frequency band of correspondingly diminished width; withthis arrangement the total widthof the frequency band employed is not vgreater than if a single drum were used at `a correspondingly:higher velocity, although the transmitting capacity, measured, vfor instance, in Words'per minute is notchanged. n

The separate transmission channels may consist in this case. of frequency bands, limitable and separable by electrical filters and Similar to those used Lin the A. C. multipletelegraphy (sound telegraphy) Consequently the side band or bands of the usual carrier wave modulation of a transmitterwould consist, in thiscase, of several ksections andeach section would be assigned a transmissionl channel.. One might consider, however, in specialcases, thepossibility of employing sevor BERLIN, GERMANY, A` CORPORATION ,or

FACSIMILE TRANSMISSION 420,330, and in Germany 'January 16, 1929.

eral transmitters with different though nearly equal carrier waves, corresponding 5to the number of collaterally operating transmissions.

In the first-mentioned case it is of advan- Y tage :to apply the one-sideband-method with suppressed carrier oscillation. In thiscase thetotalpower given off by the transmitter is applied only to the frequencies needed iforthe transmission. If it were, forinstance, neces` sary vto reduce theY speed of transmission, in view of the describedv disturbances to onethirdof its present value, thel transmitted band would vhave to consist of three sections, each containing Athe picture frequencies for one of the separate transmissions.vv Hereby only one-third of. the transmitting power'fis givenfoff through each channel, thus reducing the' intensity of reception. .However, on account of a corresponding reduction of '.the edective disturbing mirror (St'rspiegel?) at the outlet of each receiver, causedby anarrowing of its frequency 'band,.it ispossiblefto apply a higher amplification which compensates the lower transmitting power available for each channel.

y 4The above describedmethod may be ap Fig. 1 illustrates 'the transmittingand by which Fig. 2 yillustrates the receiving device. Three picture drums l, 2, 3, drivenby the same'operating mechanismand covered with the documents to ybe transmitted are spotted, that is, scanned over by a'spot-photographing device.A The driving forceI may bebfurnislied by an electro-motor 4, directly coupled to a synchronous motor 5 of constant speed, supplied with a current of normal lfrequency. This speed is reduced by means of a system of gears 6 to the 'value desired for the drums 1, 2, 3. The same mechanism drives, by means of the bevel gears 7, 8, the perforated disks 9, l0, 11 provided with a varying number of holes. The purpose of thesedisks is'to interrupt the spotting light at various frequencies. The perforated disk 9.1,nay-.generate alight to secure a helical scanning or spotting of the drums 1, 2, 3 the latter are, during the rotation, gradually advanced along their axis by means of a Worm gear 21, 22. v

With this spotting arrangement the input tubes of the three amplifiers 23, 24, 25 are subjected to modulated oscillations of a carrier frequency of 1500, 3000 and 4500 periods, With side bands Whose width depends on the spotting velocity and on the distribution of light and darkness on the documents to be transmitted. By regulating the spotting vef locity the modulation Width is kept Within the permissible limits foreach channel. Beyond theV amplifiers 23, 24, 25 filter chains or filter circuits 26, 27, 28 are provided, each of Which has to transmit only one side band of the modulation of the three carrier 4frequencies. For instance, filter 26 maytransmit the frequency band 1500 to 2500, filter 27-the band 3000 to 4000, filter 28-the band 4500 to 5500., In certain cases it is, however,

- more convenient to transmit both side bands of the carrier oscillation, provided they may be limited to such an extent as not to interfere With the neighboring transmission channel. This could be accomplished, f. i., in case themodulation Width of the mentioned carrier oscillations does not exceed 600 `periods per second. The filters 26, 27, 28 would then have to transmit, say, the frequency bands of 900 to 2100, 2400 t0 3600, 3900 to 5100. The transmitted frequencies act upon the modulating arrangement of the short- Wave transmitter 30, by Way of a common transformer 29. The detailed construction of this transnitter, of the aerials, etc., is of no importance 1ere.

The high frequency received by the short- Wave receiver 31 is at firstdemodulated in a known manner and the amplified low frequency, which is a combination of the three transmission-frequency bands, is filtered by Way of three filters 33, 34, 35. If both side bands of each carrier voscillation are passed by the filters 33, 34, 35, it is onlyvnecessary to effect by rectification a second demodulation in the amplifiers 36, 37, 38 in order to obtain directly the picture-recording frequency. If, however, only one sideband of each perforated-disk frequency is transmitted to the receiver, While the carrier oscillation is suppressed, it is necessary to generate these perforated-disk frequencies artificially. To this end frequency generators are provided, of known constrction, f. i., the interrupters 51, 52, 53, which are included in the circuit of a D. C. source 54 and are driven at constant speed over a bevel gear by a synchronous motor set 49, corresponding to the set 4, 5 at the transmitting end. The picture frequencies obtained at the outlet of the ampli-` fieis 36, 37, 38 are now transmitted to three separate recording devices. l For the sake of simplicity the recorder in this case is assumed-to `consist of an electro-chemical recording device, three recording points 39, 40, 41 gliding along a moistened, specially prepared paper Which is mounted on the three receiving drums 42, 43, 44. For this purpose it is, of course, necessary to rectify the picture frequencies. This may be effected by means of the amplifiers 36, 37, 38. The amplifiers thus serve the double purpose of reestablishing and rectifying the picture frequencies. The three drums 42, 43, 44 are driven by means of a system of gears 47 at a proper speed and advanced axially by means of aI Worm gear 45, 46 similar in construction to the operating mechanism at the transmitting end.

Instead of the electro-chemical picture recording method one may obviously apply the photographic method. In thisl case the recording points are replaced by three light relays of known construction.

Having noW described my invention, what I claim and desire to secure by Letters Patent is lie following:

A system for simultaneously transmitting a plurality of picture record messages which comprises a plurality of supporting carriers for carrying said messages, a single driving element for rotating said carriersat identical speeds relative to predetermined points positioned in like relationship With respect to each record carrier, means for illuminating related elemental areas of each of said record carriers from a plurality of light sources, means for interrupting the light from each of said light sources directed toward said record carriers at different frequencies bearing preestablished relationship one With the other, light translating means associated With each of said record carriers for converting the varying intensities of light and shadow thereon as illuminated by said light sources into proportionately modulated electric current impulses of different frequencies, means for combining the output energies of all of said light translating elements, a transmitter for transmitting said signals, means for modulating said transmitter simultaneously by all of said signals, receiving means, and means at the point of reception for separating said receivedsignals one from the other for reproducing a plurality of images corresponding to the records carried by each record carrier.

FRITZ SCHRTER. 

